Method for analysing a dental situation

ABSTRACT

A device including a camera, a processing unit and a screen. The camera configured to, at an updated instant, acquire, by a cellphone or a tablet, an updated image representing a real dental scene. The processing unit configured to determine a virtual dental scene as a representation of the real scene on the updated image and identify an element of the virtual scene which does not comply with an assessment criterion, and highlighting and/or adding a message regarding this element in the virtual scene. The screen configured to display the updated image and present the virtual scene overlaid with the representation of the real scene on the updated image displayed on the screen, in transparent mode or not on the representation. The processing unit, the camera and the screen are configured to communicate with one another. The patient acquires the updated image and observes the screen.

TECHNICAL FIELD

The present invention relates to the analysis of a dental situation of apatient.

STATE OF THE ART

When a dental care professional intervenes on the teeth of a patient orperforms a diagnosis, he or she needs to assess the real dentalsituation, and in particular the position and/or the form and/or thedimensions of the teeth and/or the good positioning of an orthodonticappliance fixed to the teeth.

This assessment generally requires a comparison of the real dentalsituation with a theoretical dental situation. For example, to diagnosethe detachment of an attachment of an orthodontic appliance, it may benecessary to compare the real dental situation in which the attachmentis abnormally separated from the tooth to which it is supposed to beglued, with a theoretical dental situation in which said attachment isactually glued to said tooth. This need exists notably in individualizedtreatments, for which the attachments are shaped to be adapted preciselyto the morphology of the teeth and/or according to the specificprescriptions of the dental care professional.

The dental care professional also performs a comparison between atheoretical dental situation and a real dental situation when seeking toassess whether a tooth is abnormally positioned or exhibits an abnormalform. The real position or form or dimension of the tooth must inparticular be compared with a theoretical position or form or dimensionthat the tooth should exhibit at the moment of comparison by the dentalcare professional.

Moreover, the analysis of the real dental situation sometimes needs tobe performed very rapidly, even in real time. For example, when thedental care professional intervenes by means of a tool to modify theform or the appearance of a tooth, the action that he or she exerciseson the tool has to be precise and be adapted in an ongoing manner to areal dental situation which changes.

Generally, the quality of the comparison between the real dentalsituation and the theoretical dental situation has an impact on thequality of the treatment, whether it be therapeutic or not.

There is therefore an ongoing need for an analysis method that allowsthe appreciation of a real dental situation, notably by a dental careprofessional, to be improved.

Moreover, the effectiveness of a dental treatment is directly linked tothe compliance by the patient with the medical prescription. Failinggood observance, the dental situation can worsen, which leads to anadditional risk for the patient, but also costs for Social Security orcare financing organizations.

Poor observance of a treatment also makes clinical studies moredifficult, particularly if the patient does not declare the periods ofnonobservance. There is therefore a need for a method that allows theobservance to be improved.

One aim of the invention is to at least partially address these needs.

SUMMARY OF THE INVENTION

The invention proposes a method for analyzing a real dental situation ofa patient, the method comprising the following successive steps:

-   -   A) at an updated instant, acquisition, preferably by means of a        camera, of an updated image representing a real dental scene;    -   B) determination of a virtual dental scene as a function of the        representation of the real dental scene on the updated image;    -   C) presentation of the virtual dental scene        -   in transparent mode and overlaid on the real dental scene,            in particular on a screen through which the real dental            scene is visible or projected onto the real dental scene, or        -   overlaid with the representation of the real dental scene on            the updated image displayed on a screen, in transparent mode            or not on said representation,    -   then, preferably, return to the step A).

In a particular embodiment, the step B) consists of a simulation, for asimulation instant, of the real dental scene represented on the updatedimage, then of a determination of a virtual dental scene as a functionof said simulation.

As will be seen in more detail hereinafter in the description, a methodaccording to the invention therefore allows the operator tosimultaneously observe

-   -   the real dental scene, directly or through a screen on the one        hand, or on the updated image on the other hand, and    -   the virtual dental scene, overlaid with the real dental scene or        with the representation of the real dental scene on the updated        image, respectively.

This overlay considerably facilitates the analysis, by the operator,preferably in real time, of the differences between the real dentalscene and the virtual dental scene. It also allows for the addition ofinformation relating to the real dental scene and for that informationto be arranged according to the representation of the real dental sceneon the updated image. The quality of the transmission of thatinformation to the operator is thereby enhanced. Finally, it allows fora realistic simulation of a dental situation, for example a simulationof an esthetic treatment.

When the method is implemented by a dental care professional, it allowshim or her to improve the quality of his or her intervention on thepatient. When it is implemented by the patient in particular, it makesit possible to realistically simulate the effect of a dental treatmentor of a modification of a dental treatment, which improves theobservance thereof.

A method according to the invention can also comprise one or more of thefollowing optional features:

-   -   in the step B), the virtual dental scene comprises        -   the representation of one or more physical elements of the            real dental scene modeled by the reference model, and/or        -   the representation of one or more physical elements of the            real dental scene not modeled by the reference model, and/or        -   the representation of one or more physical elements which            are not in the real dental scene and/or which are not in the            reference model, and/or        -   an indicator which does not represent a physical element of            the real dental scene, preferably several such indicators;    -   in the step B), an element of the virtual dental scene is        identified which does not comply with an assessment criterion,        and this element is highlighted in the virtual dental scene        and/or a message relating to said element is added to the        virtual dental scene;    -   the assessment criterion relates to the state of health of the        patient and/or to the positioning of an orthodontic appliance        worn by the patient and/or to the condition of an orthodontic        appliance worn by the patient and/or to a cost for a dental        treatment;    -   the message is an instruction to be followed by the patient        and/or by a dental care professional responsible for the        patient;    -   in the step B), the nature and/or the location and/or the        appearance of an element of the virtual dental scene, and        notably of an indicator, is determined as a function:—        -   of the context, and in particular as a function of the            distance to another element of the virtual dental scene            and/or as a function of a pursued objective;    -   in the step B), the nature and/or the location and/or the        appearance of elements of the virtual dental scene are        determined as a function of the nature and/or of the location        and/or of the appearance of elements displayed in prior virtual        dental scenes, that is to say from prior cycles of steps A) to        C), and/or as a function of the time interval with said prior        virtual dental scenes, and/or as a function of differences        between the updated images of successive cycles of the steps A)        to C);    -   in the step B), the virtual dental scene is determined in such a        way that it comprises information, notably textual or graphic,        on        -   differences between the updated image and the reference            image, and/or        -   differences between the reference model and the real dental            scene, and/or a target location, notably for a tool or an            orthodontic appliance or a decorative item;    -   in the step C), the virtual dental scene is presented on the        real dental scene or on the updated image so that the        representations of real physical elements of the virtual dental        scene are overlaid, realistically, with said real physical        elements or with the representations of said real physical        elements on the updated image, respectively;    -   a step A) is repeated less than 5 seconds after the step C),        respectively;    -   after the step C), an orthodontic appliance is modified and/or        the arch is adjusted and/or an item or an orthodontic appliance        is positioned as a function of the presentation of the virtual        dental scene on the real dental scene or on the representation        of the dental scene on the updated image.

According to an aspect of the invention, in the step C), the virtualdental scene is presented on a transparent screen, overlaid with thereal dental scene that an operator can observe through the screen, inparticular when facing the screen.

Preferably, the screen and the camera are immobilized with respect tothe operator. Preferably, they are incorporated in glasses. The methodaccording to the invention is then particularly useful for a dental careprofessional wearing the glasses to be able to assess, in real time, thedental situation of a patient that he or she is examining.

Notably according to this aspect of the invention, a method according tothe invention can be used to assess, in real time, a stripping ormilling operation, or an operation for positioning an orthodonticappliance or a part of an orthodontic appliance.

According to an aspect of the invention, in the step C), the virtualdental scene is presented, overlaid with the representation of the realdental scene on the updated image, on an opaque screen, that is to saythrough which the operator cannot see.

In one embodiment, the screen is that of a cellphone, of a tablet, of alaptop computer, or of a virtual reality headset. The screen can also bethe glass of a mirror, preferably equipped with at least one camera.

Preferably, the operator manipulates a cellphone, a laptop computer, avirtual reality headset or a mirror equipped with at least one camera,to acquire said updated image and view the real dental scene and thevirtual dental scene.

According to this embodiment, the dental care professional can work onthe arch of the patient by watching the screen. He or she then sees,simultaneously on the screen, the images acquired by the camera and theinformation supplied by the virtual dental scene. He or she can inparticular work “blind” (that is to say without seeing, directly orthrough a screen, the real dental scene), on regions of the arch that heor she cannot observe directly but that can be observed by the camera,notably when the camera is independent of the screen and, in particular,when the camera can be introduced into the mouth of the patient.

In one embodiment, in the step B) or d), the virtual dental scene isdetermined as a function of a value of at least one treatment parameterthat can be modified by interaction with said cellphone, said laptopcomputer, said virtual reality headset, said camera, said mirror or saidglasses, preferably with the cellphone. Preferably, the treatmentparameter relates to the wearing of an orthodontic appliance by thepatient and/or to the observance of a treatment instruction by thepatient.

A method according to the invention, notably according to this aspect ofthe invention, can facilitate the decision-making by the patient, inparticular because it allows him or her, by choosing the simulationinstant, to view the effect, on his or her appearance, of the possibledifferent treatment options. The method can also be an efficientteaching tool to improve observance.

Use of a Reference Model

In a preferred embodiment, the virtual dental scene is determined bymeans of a three-dimensional digital model digitally modeling at leastone arch of the patient, called “reference model”.

Preferably, the reference model is used also, in the step C), toposition the virtual dental scene with respect to the real dental sceneor the representation thereof.

Advantageously, the composition of the virtual dental scene can thus beentirely automated.

The method according to the invention can in particular comprise thefollowing successive steps:

-   -   a) at a reference instant, generation, preferably by means of a        scanner, of a reference model digitally modeling at least one        dental arch of the patient;    -   b) optionally, modification of the reference model;    -   c) at an updated instant, acquisition, preferably by means of a        camera, of an updated image representing a real dental scene;    -   d) search, by observation of the reference model, optionally        modified, for a reference image presenting a maximum match with        the updated image, then determination, as a function of the        reference image, of a virtual dental scene;    -   e) presentation of the virtual dental scene        -   in transparent mode and overlaid on the real dental scene,            in particular on a screen through which the real dental            scene is visible or projected onto the real dental scene, or        -   overlaid with the representation of the real dental scene on            the updated image displayed on a screen, in transparent mode            or not on said representation,    -   then, preferably, return to the step c).

The step c) is a particular case of step A). The optional featuresapplicable to the step A) are therefore applicable to the step c).

The steps a), b) and d) constitute together a particular case of stepB). The optional features applicable to the step B) are thereforeapplicable to the steps a), b) and d).

The step e) is a particular case of step C). The optional featuresapplicable to the step C) are therefore applicable to the step e).

Preferably, in the step a), an arch of the patient or a physical modelof said arch is scanned while said arch or said physical model of saidarch is wearing or not wearing an orthodontic appliance, and inparticular while said arch or said physical model of said arch is notwearing an orthodontic appliance.

The updated instant can be different from the reference instant, and inparticular be more than 3 days after the reference instant. The methodcan then be used to view the modifications of the arch between these twoinstants.

In one embodiment, the virtual dental scene consists of the referenceimage.

Preferably, in the step d), the nature and/or the location and/or theappearance of an element of the virtual dental scene, and notably of anindicator, is determined as a function:

-   -   of the reference image, and/or    -   of differences between the updated image and the reference        image, and/or    -   of the context.

The reference model can give access to “hidden” information, that is tosay information not accessible to the operator or that is difficult toaccess by the operator. Such hidden information can in particular dependon the reference image, and therefore on the updated image. In oneembodiment, at least a part of the hidden information is selected in thestep d). The step d) thus makes it possible to create a virtual dentalscene which contains such information and the step e) allows it to bepresented on the real dental scene or on the representation thereof.

Applications

A method according to the invention can in particular be used fornon-therapeutic purposes, in particular for research purposes, forexample to assess the efficiency of a treatment or of an orthodonticappliance, or for esthetic purposes, or for teaching purposes.

In one embodiment, the virtual dental scene can relate to the realdental scene as simulated at a simulation instant or, for the past, asobserved at a simulation instant. In particular, the virtual dentalscene can simulate the real dental scene at the simulation instant. Thesimulation is preferably obtained by means of a computer, preferably bymeans of an artificial intelligence algorithm.

The method according to the invention is then particularly useful for anoperator, and in particular a patient, to be able to view a dentalsituation at a prior simulation instant or, preferably, after theupdated instant, or view the evolution of such a dental situation byvarying the simulation instant.

Preferably, the method comprises a series of cycles of steps A) to C),or c) to e), the virtual dental scene being determined, on each cycle,to simulate a dental situation at the current simulation instant.

In one embodiment, the virtual dental scene is determined by means of adynamic simulation tool configured to supply at least one element of thevirtual dental scene as a function of a determined simulation instant,in particular as a function of a simulation instant after the updatedinstant.

When it is used for simulation purposes, a method according to theinvention can comprise one or more of the following optional features:

-   -   the simulation instant is after the updated instant, for example        more than 1 day, 10 days or 100 days after the updated instant;    -   the simulation instant is determined before the step A) or        before the step B), preferably by interaction of the operator        with a screen;    -   said screen        -   is a touch screen and the time interval between the updated            instant and the simulation instant is modified by            interaction, preferably by dragging, of a finger over said            screen, and/or        -   comprises a field for inputting the simulation instant;    -   between two cycles of steps A) to C), the time interval between        the updated instant and the simulation instant is modified;    -   the simulation instant is set by modifying the position of a        cursor represented on the screen;    -   in the step B), the nature and/or the location and/or the        appearance of an element of the virtual dental scene, and        notably of an indicator, is determined as a function:—        -   of the context, and in particular as a function of the            distance to another element of the virtual dental scene            and/or as a function of a pursued objective, and/or as a            function of the simulation instant;    -   in the step B), a color and/or a form and/or a position of a        visible or invisible part of the mouth, preferably of a jaw, of        a dental crown and/or of a dental root and/or of the gum of the        patient, are determined for the simulation instant, and the        virtual dental scene is determined in such a way that it        reproduces said color and/or form and/or position;    -   the patient acquires said updated image in the step A), and        observes the screen in the step C).

Such a method according to the invention can in particular be used tosimulate:

-   -   the effect of one or more orthodontic appliances on the teeth of        the patient, notably in order to choose the one best suited to        him or her;    -   the effect of a temporary or permanent stop to a current        treatment;    -   the effect of an application of an instruction.

Notably, the method can be used, notably for teaching purposes, to viewthe effect of a modification of the frequency and/or of the durationand/or of the technique for brushing of the teeth, or the effect of adelay in changing an orthodontic splint and/or of a delay in making anappointment with the dental care professional.

For example, it can be used to simulate, at the simulation instant, thecolor and/or the position of the teeth of the patient. Notably, it canbe used to view the effect of a treatment for whitening the teeth or theeffect of cigarettes.

When the method comprises the steps a) to e), in the step b), thereference model can be modified to simulate the effect of the flow oftime between the reference instant and the simulation instant, and inparticular the effect of a dental treatment, therapeutic or not, betweenthese instants.

A method according to the invention can even notably be used to:

-   -   assess a difference relating to the position and/or the form        and/or a dimension of one or more teeth and/or of an orthodontic        appliance between the reference instant and the updated instant,        or between the simulation instant and the updated instant,        notably in the context of an orthodontic treatment, and/or    -   indicate a target location of the dental arch, in particular on        one or more teeth.

A method according to the invention can in particular be used to view astripping undergone by a tooth or a distortion of the gum between thereference and updated instants or between the simulation instant and theupdated instant, or guide the placement of an orthodontic appliance orof a part of an orthodontic appliance or of a dental implant or of adecorative item.

In one embodiment, the virtual dental scene relates to the real dentalscene, preferably at least partly represents the real dental scene as itappears at the updated instant or as it should appear at the updatedinstant according to a simulation. In other words, if the virtual dentalscene represents the teeth of the patient, it represents them in theirposition at the updated instant or in their simulated position at theupdated instant. The simulation instant is therefore identical or closeto the updated instant, for example separated from the updated instantby less than 1 month, less than 2 weeks or less than 1 week.

Device

The invention relates also to a device for implementing a methodaccording to the invention.

Such a device comprises

-   -   optionally, means for generating and optionally modifying a        reference model in the steps a) and b), this means preferably        comprising a scanner and a computer;    -   a camera configured to implement the step A) or c);    -   a processing unit configured to implement the step B) or the        step d);    -   presentation means configured to implement the step C) or e),        and preferably a screen as described previously;        the processing unit, the camera and the presentation means being        configured to communicate with one another to implement said        steps.

Preferably, the camera is configured so as to acquire a succession ofupdated images of the real dental scene and transmit said updated imagesto the processing unit.

Preferably,

-   -   the processing unit is configured to:        -   search, for each updated image received from the camera, by            observation of a reference model, for a reference image            presenting a maximum match with said updated image,        -   determine, as a function of the reference image, a virtual            dental scene, and        -   transmit said virtual dental scene to the presentation            means;    -   the presentation means are configured to show the virtual dental        scene overlaid on the real dental scene or on the representation        of the real dental scene in the updated image.

In one embodiment, the virtual dental scene is presented in transparentmode on the real dental scene or on the representation thereof in theupdated image.

In one embodiment, the device comprises glasses in which the camera andthe presentation means, preferably the camera, the presentation meansand the processing unit, are incorporated.

In one embodiment, the presentation means are configured to present thevirtual dental scene on a lens of the glasses, realistically overlaidwith the real dental scene or to project the virtual dental scene ontothe physical elements which constitute the real scene.

In one embodiment, the device comprises a cellphone or a camera or alaptop computer or a virtual reality headset or a tablet or a mirror, inwhich the camera and the presentation means, preferably the camera, thepresentation means and the processing unit, are incorporated.

The presentation means preferably comprise a screen that makes itpossible to display the updated image and present the virtual dentalscene on the representation of the real dental scene, in “augmentedreality”.

The representation of the real dental scene can be an image displayed onthe screen of the cellphone or of the camera or of the laptop computeror of the virtual reality headset or of the tablet.

The representation of the real dental scene can be the reflectionreturned by the mirror.

As will be seen in more detail hereinafter in the description, theobserver can thus observe the real dental scene or the representationthereof on the updated image and the virtual dental scene, preferably intransparent mode, on the real dental scene or on the representationthereof on the updated image. He or she can thus immediately have accessto the information contained in the virtual dental scene, presented inthe environment of the real dental scene. The incorporation of thescreen in the glasses is particularly advantageous for this purpose.

Definitions

A “patient” is a person for whom a method according to the invention isimplemented, independently of whether or not this person is following adental treatment.

A “dental situation” defines a set of characteristics relating to anarch of a patient at an instant, for example the position of the teeth,their form, the position of an orthodontic appliance, etc. at thatinstant.

A “dental care professional” is understood to mean any person qualifiedto deliver dental services, which includes an orthodontist and adentist. The operator wearing the glasses is preferably an orthodontistor a dentist.

“Operator” is understood to mean the person who implements the methodfor the virtual dental scene to be presented to him or her in the stepC). The operator can in particular be the patient or the dental careprofessional.

“Glasses” are understood to mean an appliance which can be worn in frontof the eyes of an operator, preferably resting on the nose and/or theears of the operator.

An “orthodontic appliance” is an appliance worn or intended to be wornby a patient. An orthodontic appliance can be intended for a therapeuticor prophylactic treatment, but also for an esthetic treatment. Anorthodontic appliance can be in particular an appliance with arch andattachments, or an orthodontic splint. Such a splint extends in such away as to follow the successive teeth of the arch to which it is fixed.It defines a generally “U”-shaped channel. The configuration of anorthodontic appliance can be in particular determined to ensure thefixing thereof to the teeth, but also as a function of a targetpositioning desired for the teeth. More specifically, the form isdetermined so that, in the service position, the orthodontic applianceexerts strains tending to move the teeth being treated to their targetpositioning (active orthodontic appliance), or to keep the teeth in thistarget positioning (passive orthodontic appliance, or “restraining”orthodontic appliance).

“Model” is understood to mean a digital three-dimensional model.

“Image” is understood to mean a two-dimensional image. An image isformed by pixels. The “updated images” are images taken at a so-called“updated” instant. They are preferably extracted from a film taken by acamera. A “reference image” is a view of a “reference” model whichpresents a maximum match with an updated image.

“Arch” is understood to mean all or part of a dental arch. An “image ofan arch”, or “model of an arch”, is thus understood to mean arepresentation in two or three dimensions, respectively, of all or partof said arch.

A “scene” consists of a set of elements which can be observedsimultaneously. A “dental scene” is a scene comprising an arch.

A “real scene” consists of physical elements. A real dental scenetherefore comprises an arch, but also, optionally, an orthodonticappliance worn by the teeth of the arch or manipulated by the operator,and/or a tool manipulated by an operator.

A “virtual scene” consists of representations of elements, notablyrepresentations

-   -   of a physical element of the corresponding real dental scene        (that is to say of the real dental scene represented on the        updated image from which the virtual dental scene was        determined) or    -   of another item of information, or “indicator”.

A physical element can be modeled by the reference model, for example atooth outline, or not modeled by the reference model, for example a toolmanipulated by the operator.

A representation of a physical element is not necessarily realistic. Forexample, a tool can be symbolized by a straight line.

The presentation of a virtual dental scene is “in transparent mode” on areal dental scene when it allows the operator to see, through saidvirtual dental scene, the real dental scene.

The presentation of a virtual dental scene is “in transparent mode” onan updated image representing a real dental scene when it allows theoperator to see the updated image through said virtual dental scene.

A virtual dental scene is displayed “overlaid” or “in register” with areal dental scene or with a representation of a real dental scene on anupdated image when it comprises representations of physical elements ofthe real dental scene which are presented in such a way that theoutlines of said representations, possibly transparent, are overlaid onthe outlines of said physical elements or of said representations ofsaid physical elements on the updated image, respectively. The overlaythus appears realistic. For example, when the observer observes a toothof a dental arch, the presentation is determined so that therepresentation of the tooth on the virtual dental scene is overlaid onthe view of that tooth perceived by the operator.

The “location” of an element of the virtual dental scene refers to itsposition with respect to the elements of the real dental scene or of therepresentation of these elements on the updated image when the virtualdental scene is presented in the step C).

The “match” (or “fit”) between two objects is a measurement of thedifference, or “distance”, between these two objects.

Preferably, two images or “views” which present a maximum matchrepresent substantially the same elements in the same way. In otherwords, the representations of the elements on these two images can besubstantially overlaid.

“Comprise” or “include” or “present” or “represent” should beinterpreted without restriction, unless indicated otherwise.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will become more apparenton reading the following detailed description and on studying theattached drawing in which:

FIG. 1 represents, schematically, the different steps of an analysismethod according to a preferred embodiment of the invention;

FIG. 2 represents an example of a reference image of a reference model;

FIGS. 3 a-3 b illustrate the processing of a reference image to extracttherefrom a reference map representing outline information;

FIGS. 4 a and 4 b illustrate the processing of an updated image toextract therefrom an updated map representing outline information;

FIGS. 5, 6 and 7 schematically illustrate examples of devices accordingto the invention;

FIG. 8 represents the overlay of a virtual dental scene on an updatedimage.

Identical references are used to designate members that are identical orsimilar in the different figures.

DETAILED DESCRIPTION

Device

A device 10 according to the invention comprises a camera 16, a computerprocessing unit 12 and presentation means 18. The camera 16, theprocessing unit 12 and the presentation means are provided with meansallowing them to communicate with one another.

As represented in FIGS. 5, 6 and 7 , the camera 16 and/or the processingunit 12 and/or the presentation means can be incorporated in glassesconventionally comprising a frame 14 configured to be worn by the noseand the ears of an operator, in a cellphone, in a tablet, in a laptopcomputer, in a virtual reality headset, in a camera or in a mirror 17.

The camera 16 is intended to acquire updated images representing thereal dental scene observed by the operator through the glasses (FIG. 5 )or on the screen of a cellphone (FIG. 6 ) or of a laptop computer, of avirtual reality headset, of a camera or of a tablet, or on the glass 19of the mirror (FIG. 7 ). It can be a conventional camera.

In one embodiment, the device comprises means for projecting structuredlight patterns, for example a cloud of dots, for example laser, inparticular infrared. Advantageously, the real dental scene reveals thesepatterns in a distorted manner, which allows information relating todepth to be deduced therefrom.

In the case where the device comprises a mirror, the glass 19 can be aglass without silvering and the camera can be arranged behind the glass,as in FIG. 7 .

In one embodiment, the device comprises several cameras, which makes itpossible, by simple trigonometric calculation, to assess the distancebetween the objects observed and the camera. The multiplicity of thecameras thus makes it possible to speed up the search for the referenceimages. The cameras thus also make it possible to simulate thethree-dimensional view that the observer has of the real dental scene.

“Presentation means” is understood to mean any means configured toreceive, from the processing unit 12, a virtual dental scene, and showsaid virtual dental scene on the real dental scene, on a screen throughwhich an observer can see the real dental scene or on the updated image.

In one embodiment, the presentation means 18 comprise a screen and aprojector for projecting the virtual dental scene onto the screen.

Particularly in the embodiment in which the camera is incorporated inglasses, the screen can be transparent. It is preferably fixed to theframe 14, and the virtual dental scene is presented on the screen inorder for the operator to see, by observing this screen, not only thereal dental scene through the screen, but also the virtual dental sceneprojected onto the screen.

The glasses conventionally comprise two lenses which extend in front ofthe two eyes of the operator, respectively, but the number of lenses isnot limiting. The lenses can be vision-corrective or not. Several lensescan extend in front of one and the same eye. For example, a first lenscan correct the view of the operator and a second lens can be a lensserving as screen.

The HoloLens appliance, developed by the company Microsoft®, is anexample of presentation means.

The screen can be opaque and the updated image and the virtual dentalscene are presented on the screen, in register, in order for theoperator to see, by observing this screen, not only the updated imagerepresenting the real dental scene, but also the virtual dental scene.

In this embodiment in particular, the camera can be immobilized withrespect to the screen, for example when the camera and the screen areincorporated in a cellphone (FIG. 6 ) or a laptop computer or a virtualreality headset or a camera or a tablet or a mirror.

Alternatively, the camera can be free (or “independent”) with respect tothe screen. Advantageously, this latter embodiment allows for greatflexibility. For example, in one embodiment, the camera can beintroduced into the mouth while the screen remains outside the mouth.

Particularly in the embodiment in which the camera is incorporated in amirror or is secured to a mirror, the screen can be the reflecting glass19 of the mirror, and the virtual dental scene can be presented on thescreen, in register with the reflection R returned by the glass 19, inorder for the operator to see, by observing this screen, not only thereflection R representing the real dental scene, but also the virtualdental scene overlaid on the real dental scene.

The reflection, like the updated image displayed on the screen of theglasses, of the cellphone, of the laptop computer, of the virtualreality headset, of the camera or of the tablet, thus gives the operatora representation of the real dental scene.

The processing unit 12 can comprise the conventional electronic means ofany computer, and in particular a central processing unit 22, a programand a memory 24. The memory 24 preferably contains a reference model ofat least a part of the real dental scene, and in particular a model ofthe dental arch, for example as represented in FIG. 2 . The programcomprises code instructions that make it possible, when they areexecuted, to implement the step d), and in particular to analyze anupdated image, to search for a view of the reference model whichpresents a maximum match with the updated image, that is to say areference image, then to determine, accordingly, a virtual dental scene.

In one embodiment, the device also comprises an interface allowing anoperator to parameterize the virtual dental scene. Preferably, theinterface is configured for an operator to be able to modify asimulation instant determining the virtual dental scene. The content ofthe virtual dental scene can in particular consist of the representationof elements of the real dental scene under an appearance and/or at aposition that are simulated for the past or future simulation instant orknown at a past simulation instant.

For example, in one embodiment, the screen is a touch screen and theoperator can modify the simulation instant by entering a date in aninput field or by moving one or more fingers over the screen. Forexample, a movement to the right of the screen can result in an advanceto the future and a movement to the left of the screen can result in amovement back to the past. The virtual dental scene presented is adaptedaccordingly, preferably in real time.

The interface can also be a mechanical member, for example a button or athumbwheel.

In one embodiment, the device is configured for the time intervalbetween the updated instant and the simulation instant to changecontinually from one cycle to another, that is to say for the successionof cycles of steps A) to C) or c) to e) to simulate an advance in timeor a return in time. In one embodiment, the time difference between twosuccessive simulation instants is constant, which makes it possible toview a change in which the time flows at a constant speed.

The processing unit determines the conditions in which the virtualdental scene must be presented to appear, to the operator, overlaid withthe real dental scene.

When the virtual dental scene has to be presented on the updated imagedisplayed on a screen, the operator observes the screen and thereforesees what is observed by the camera. Simple operations, such as scaling,a correction of the perspective effects or a realignment on the updatedimage, can be sufficient to ensure a realistic overlay of the virtualdental scene on the updated image, for example by using characteristicmarks, as described hereinbelow.

When the virtual dental scene has to be presented on a transparentscreen through which an operator observes the real dental scene, it ispreferable for the camera to be arranged so as to capture an updatedimage which corresponds to the view of the real dental scene by theobserver. It is also preferable for the screen to be at a constantdistance, and oriented in a fixed manner with respect to the observer.Advantageously, the processing unit can thus easily determine, from theupdated image acquired by the camera, the view of the real dental sceneobserved by the operator, and the conditions in which the virtual dentalscene must be presented to appear, to the operator, overlaid with thereal dental scene.

Method

A method according to the invention can be implemented by means of adevice according to the invention.

In the step a), at a reference instant, a reference model is generated,preferably by means of a scanner.

The reference model can be a model of the arch of the patient or becomposed of a model of this arch and of a model of an orthodonticappliance arranged on said model of the arch.

The creation of the reference model results preferably from the takingof measurements.

Preferably, an arch of the patient is scanned with a 3D scanner,optionally while the patient is wearing an orthodontic appliance, or amolding of this arch, so as to create a reference model. Preferably, thescan is performed with a conventional 3D scanner.

The reference model obtained by means of a scanner represents an arch,but also, if necessary, any object scanned at the same time as the arch,for example an orthodontic appliance or a decorative item fixed to thearch.

The reference model can alternatively be a generic arch model, chosenfrom a base of generic models, that is to say an arch model that isapplicable, roughly, to several patients, or result from a distortion ofsuch a generic model. The distortion can in particular be as a functionof measurements or of observations made on the patient, for example as afunction of photos of his or her dental arches. The distortion of amodel in order for it to be able to correspond to one or more photos canimplement a metaheuristic method, as described notably in WO2016/066651.

A generic arch model can in particular be a model obtained by astatistical processing, for example an average, over more than 5, morethan 10, more than 100 or more than 1000 historical models generated bymeans of a scanner. The historical models are preferably models ofdental arches of “historical” patients having dental characteristicsidentical or similar to those of the patient for whom the referencemodel is being generated, for example who have suffered the samepathology and/or have the same age and/or have the same sex and/or havea similar morphology.

The reference model, three-dimensional, can be observed from any angle.An observation of the model, from an angle and at a distance that aredetermined, is a “view of the model”. FIGS. 2 and 3 a are examples ofviews of a reference model.

The views of the reference model are intended to be compared with theupdated images in order to determine, for each updated image, areference image that most closely resembles the updated image, thenconsequently construct a virtual dental scene adding informationrelating to the elements represented on the updated image.

The reference instant can be close to the updated instant, for exampleseparated (after or before) by less than 1 month, 2 weeks or 1 week or 3days from the updated instant. Updated images can then be used todistort a generic model until the reference model corresponding to thedental situation at the updated instant is obtained. Moreover, thevirtual dental scene then provides information on the dental situationspecific to the updated instant. For example, if the reference modelmodels the roots of the teeth, the virtual dental scene can representthe roots of the teeth.

The reference instant can be separated from the updated instant, forexample separated by more than 1 month, 2 weeks or 1 week or 3 days fromthe updated instant. The reference model can then differ substantiallyfrom the reality at the updated instant. The information supplied by thevirtual dental scene can then relate to the change to the dentalsituation between the reference instant and the updated instant. Forexample, they can provide information on a movement of the teeth or ofan orthodontic appliance.

For example, the method can be used to check whether a passiverestraining appliance correctly holds the teeth in position after adental treatment. The reference model can be generated immediately afterthe fitting of the appliance and the acquisition of an updated image cantake place one month after this fitting. The reference image and thevirtual dental scene will therefore concern the teeth in their positionat the end of treatment and the presentation of the virtual dental sceneon the real dental scene, at the updated instant, will thus allow thedental care professional to detect the differences with their realpositions.

In the step b), in one embodiment, the reference model is modified.

The modification can be performed at any moment between the referenceinstant and the updated instant. Preferably, it is performedsubstantially at the reference instant.

The modification of the reference model can be a distortion of thismodel.

In one embodiment, the reference model is segmented, and in particulartooth models are created, as described in WO 2016/066651. Then, thetooth models are moved or distorted.

The modification in the step b) can simulate the effect of the flow oftime, for example the effect of a dental treatment, between thereference instant and the updated instant. The modification of thereference model thus results in a model representing the teeth in aposition or a form estimated for the updated instant.

The movement or the distortion of the tooth models can also bedetermined or refined on the basis of one or more updated images, asdescribed in WO 2016/066651. Preferably, the initial reference model,determined in the step a), then results from measurements by means of ascan of at least one arch or of at least one molding of an arch.

The method can thus be used to check whether the progress of a dentaltreatment is as predicted, the initial reference model being modified tocorrespond to the situation anticipated at the updated instant. Inorthodontics, substantial changes can take a few days. Preferably, inthis embodiment, the time interval between the updated instant and thereference instant is greater than 3 days, even greater than 1 week,greater than 2 weeks, greater than 4 weeks, greater than 8 weeks,greater than 12 weeks, even greater than 16 weeks.

The reference image, resulting from an observation of the modifiedreference model, then reveals the teeth in their positions or formsanticipated at the updated instant. It constitutes or can beincorporated in a virtual dental scene whose presentation, in the stepe), allows the dental care professional to detect the differencesbetween the real positions or forms of the teeth and the positions orforms anticipated for the updated instant.

The modification of the initial reference model can consist of anaddition of another model and/or of the modification of this othermodel. For example, a model of an orthodontic appliance fitted onto thearch can be added to a reference model which might initially representonly the arch. The modification of the reference model can then includea modification of this orthodontic appliance for it to appear in itsposition or form anticipated for the updated instant. The presentationthereof, in the step e), then allows the dental care professional todetect the differences between the real position or form of theorthodontic appliance and the position or form anticipated for theupdated instant, and notably to detect any separation of an attachment.

In the step c), at the updated instant, an updated image is acquiredwith the camera that represents a real dental scene. In the figures, theupdated image is represented by a continuous line on the screen 18.

A device according to the invention in which the camera is fixed ontothe frame of glasses or is incorporated in a mirror makes it possible toacquire an updated image which represents with great accuracy the realdental scene observed by the operator through the lenses of theseglasses or on this mirror.

A device according to the invention in which the camera is incorporatedin a cellphone, a laptop computer, a tablet or a camera makes itpossible to acquire an updated image which exactly represents the realdental scene observed by the operator on the screen of the cellphone, ofthe computer, of the tablet, or of the camera, respectively.

With a virtual reality headset in particular, the camera can be rigidlysecured to or be independent of the screen. The independence of thecamera and of the screen advantageously allows the operator to operatewithout directly seeing the real dental scene, that is to say by seeingit only on the screen. He or she can thus work “blind”.

Preferably, the updated image is in color, preferably in real colors.

In the step d), a reference image is sought which presents a maximummatch with the updated image.

In the step d), all the known methods for producing a maximum match canbe envisaged.

A maximum match can be obtained notably as a result of an optimizationso as to minimize said distance (“best fit”).

Preferably, the reference image is sought by observing the referencemodel from different observation angles and different distances, until aview of the reference model is obtained which corresponds substantiallyto the updated image, that is to say which can be substantially overlaidon it. For each updated image, a reference image is thus obtained thatpresents a maximum match with the updated image. This search ispreferably performed by means of a metaheuristic method, preferablyevolutionist, preferably by simulated annealing.

The metaheuristic methods are known optimization methods. They arepreferably chosen from the group formed by

-   -   the evolutionist algorithms, preferably chosen from among:        evolution strategies, genetic algorithms, differential evolution        algorithms, distribution estimation algorithms, artificial        immune systems, path recomposition, shuffled complex evolution,        simulated annealing, ant colony algorithms, particle swarm        optimization algorithms, tabu search, and the GRASP method;    -   the kangaroo algorithm,    -   the Fletcher and Powell method,    -   the sound effects method,    -   stochastic tunneling,    -   random restart hill climbing,    -   the cross-entropy method, and    -   hybrid methods of the metaheuristic methods cited above.

The exploration of the reference model to search for the reference imagecan comprise one or more of the features of the steps c), d) and e) ofWO 2016/066651, in as much as they relate to such exploration.

Preferably, the updated image is processed to produce an updated maprepresenting, at least partially, discriminating information, and saidsearch comprises the following steps:

-   -   i) acquisition of a view of the reference model;    -   ii) processing of the view to produce at least one reference map        representing, at least partially, the discriminating        information;    -   iii) comparison of the updated and reference maps so as to        determine a distance between said updated and reference maps        and, if the distance is greater than a threshold, modification        of the view, then return to the step ii).

The updated and reference maps represent the same discriminatinginformation. The discriminating information is characteristicinformation which can be extracted from an image (“image feature”),conventionally by computer processing of this image. It is preferablychosen from the group consisting of outline information, colorinformation, density information, distance information, brightnessinformation, saturation information, information on glare andcombinations of such information.

The person skilled in the art knows how to process an image to revealthe discriminating information, and therefore create the correspondingmap.

For example, FIG. 4 b is an updated map relating to the outline of theteeth obtained from the updated image of FIG. 4 a . FIG. 3 b is areference map relating to the outline of the teeth obtained from theview of FIG. 3 a.

The modification of the view is preferably guided by heuristic rules,for example by favoring the modifications which, according to ananalysis of the preceding distances, appear the most favorable to reduceit.

The step iii) culminates in a reference image that can substantially beoverlaid on the updated image.

A maximum match between the reference image and the updated image can beobtained also as a result of the overlaying of identified markers onthese two images, for example the overlaying of fixed markers like theend of a tooth or a point of contact between two teeth.

The virtual dental scene preferably comprises, or consists of, thereference image. The reference image is a particular example of avirtual dental scene.

In FIG. 8 , the elements of the virtual dental scene are represented bydotted lines.

In a preferred embodiment, a virtual dental scene comprises arepresentation, preferably realistic, of one or more elements of thecorresponding real dental scene. In particular, preferably, it comprisesa representation of the arch, but also optionally, for example, arepresentation of an orthodontic appliance worn by the teeth of the archor that the operator manipulates in front of the arch, or of a tool thatthe operator manipulates in front of the arch.

As represented in FIG. 8 , the virtual dental scene can for examplerepresent the outlines 26 of the teeth and its projection onto the teethcan facilitate the detection of movements or of distortions of theteeth.

The virtual dental scene can also comprise the representation of one ormore physical elements of the real dental scene not modeled by thereference model, for example a tool 28 manipulated by the operator. Toidentify such physical elements, the updated image is analyzed, forexample by means of artificial intelligence algorithms.

The virtual dental scene can also comprise the representation of one ormore physical elements which are not in the real dental scene, forexample a tool or an orthodontic appliance or a decorative item 32, forexample positioned on the virtual dental scene so as to appear, on thereal dental scene, at a location (“target placement”) where the tool orthe orthodontic appliance or the decorative item, respectively, ought tobe arranged by the dental care professional or by the patient.

The representation of a physical element can be realistic, for exampleconsist of the outlines of the physical element considered, or symbolic.For example, the bit of a drill can be symbolized by an arrow.

The representation of the physical elements of the virtual dental scenecan be two-dimensional and/or three-dimensional. The presentation of thevirtual dental scene can be in particular a hologram.

The virtual dental scene can also comprise, in addition or alternativelyto the representation of physical elements, for example of the referenceimage, one or more indicators 34.

An indicator is an element of a virtual dental scene which does notrepresent, even symbolically, a physical element of the real dentalscene.

An indicator can in particular be a text or a symbol (a dot, a line, anarrow, a color control patch, etc.), for example a symbol illustratingdifferences between the updated image and the reference image, or thatprovides information relating to a deed performed by the operator, forexample indicating to him or her a direction for a tool that he or sheis manipulating.

In one embodiment, the indicator points to a location to which theoperator must pay particular attention, for example a brushing. Theindicator can be an image, preferably playful, for example a drawing ofa monster or of a microbe, to which the operator must apply a tool, forexample a toothbrush. Such an indicator improves the learning ofbrushing of teeth, for example.

In FIG. 8 , the indicator 34 points to a dental region which has beenabraded.

The nature of an indicator can be determined as a function of thereference image. The indicators can in particular be associated with thereference model or with a region of the reference model. They are forexample stored in a database in the memory 24 of the processing unit.

For example, additional information can be associated with differentregions of the reference model, for example to indicate decay, brittlezones, or bonding zones for an orthodontic appliance. Additionalinformation can also be associated with the reference model as a whole,for example to specify the circumstances of its production orinformation on the patient or on the orthodontic appliance possiblyrepresented. The indicators make it possible to present such additionalinformation.

The nature of an indicator can be determined as a function of thedifferences between the updated image and the reference image.

For example, indicators can be added to reveal a distortion or amovement of a tooth, or a detachment of an orthodontic appliance.

The nature and/or the location and/or the appearance of an indicator canbe determined as a function of the context, and in particular as afunction of the distance to another element of the virtual dental sceneand/or as a function of a pursued objective. For example, it will appearwith an appearance that is a function of the distance to a particulartooth or a function of the risk for the patient.

The context is defined by the conditions in which the method is used.

For example, the operator can have the objective of checking thepositioning of the orthodontic appliance worn by the patient. Theindicators which are not linked to this check, for example theindication of the zones of decay, are not then necessary.

In one embodiment, before the step d), the operator inputs additionalinformation into the database, as a function of the use of the targetedmethod. For example, he or she specifies a location for attaching adecorative item or for milling a tooth. The corresponding indicators canadvantageously be added to the virtual dental scene.

For example, an arrow can point to a zone of a tooth in order toindicate to the operator the point where an orthodontic appliance or adecorative item must be fixed, or on which he or she needs to act, forexample by means of a tool such as a burr.

An indicator can also represent, realistically or not, a non-visiblepart of a physical element of the real dental scene (and which, notbeing visible to the operator, therefore does not belong to the realdental scene), for example a root of a tooth, a bone or a dental nerve.

The elements which make up the virtual dental scene are positioned inthis scene as a function of the elements of the real dental scene, andtherefore, in this particular case, as a function of the referenceimage. In particular, the representations of real physical elements arepreferably positioned in the virtual dental scene so that, in the stepe), they are overlaid, accurately, with these real physical elements orwith their representations on the updated image.

Likewise, an indicator adding specific information to a physicalelement, for example specific to a tooth, is preferably positioned sothat, in the step e), it appears in immediate proximity to or overlaidon this physical element, for example on this tooth.

Indicators can be arranged so as to be displayed, in the next step, atthe points where differences have been identified between the referenceimage and the updated image. For example, a red mark can be displayed atthe locations where an orthodontic appliance has come unstuck from theteeth.

In one embodiment, the context is changing and the nature and/or thelocation, in the virtual dental scene, of the indicators are adaptedaccordingly. In particular, the nature and/or the location of theindicators can be determined as a function of the nature and/or of thelocation of indicators displayed in prior virtual dental scenes, that isto say scenes determined in preceding cycles c)-e) (or A) to C)), and/oras a function of the time interval with said prior virtual dentalscenes, and/or as a function of differences between the updated imagesof successive cycles c)-e) (or A) to C)).

For example, the method can be used to guide an action of the operatorwith a tool, for example drilling by means of a drill. An element of thevirtual dental scene can be an arrow indicating the orientation of thedrill and the position of its free end. The database can contain aprotocol setting, for example, the point of penetration into the tooth,the trajectory and the optimal speed of advance of the drill. On eachcycle of the steps c) to e) (or A) to C)), the location of the elementin the virtual dental scene is then determined as a function of itslocation in the virtual dental scenes determined previously and,preferably, as a function of the time interval between said virtualdental scene and said prior virtual dental scenes.

Also preferably, the tool, for example the drill, which appears on thesuccessive updated images, is identified on these images and thelocation of the element in the virtual dental scene is adapted to takeaccount of the real position of the tool. Advantageously, therepresentation of the indicator in the virtual dental scene cantherefore change as a function of the real position of the tool.Notably, it can thus be adapted to the actual rate of progress or to theactual trajectory of the tool.

In one embodiment, the appearance of an element of the virtual dentalscene changes as a function of the context.

For example, an element of the virtual dental scene is identified whichdoes not comply with an assessment criterion, for example because itexceeds a risk threshold, then attention is drawn to this element in thevirtual dental scene. For example, the color of the element can bemodified if the analysis of the context shows that the situation isbecoming dangerous, for example because the tool is not following thedesired trajectory or because the orthodontic appliance would result inan excessive correction of the positioning of the teeth.

In one embodiment, the virtual dental scene does not include thereference image. The reference image can be used to determine the natureand/or the location of the elements in the virtual dental scene.However, it is not presented to the observer in the step e) (or C)).

In one embodiment, the virtual dental scene is determined as a functionof a past or future simulation instant. In particular, it can comprise arepresentation, preferably realistic, of one or more elements of thecorresponding real dental scene in a past or future configuration.

In one embodiment, it comprises a representation of the arch and/or arepresentation of an orthodontic appliance worn by the teeth of the archas measured or simulated at a past simulation instant.

In one embodiment, it comprises a representation of the arch and/or arepresentation of an orthodontic appliance worn by the teeth of the archas anticipated for a future simulation instant.

The simulation at a past or future simulation instant can be performedby any simulation software or by an operator, for example by a dentalcare professional.

The virtual dental scene can for example represent the outlines of theteeth, the positioning of an orthodontic appliance or the color of theteeth at the simulation instant. The presentation of the virtual dentalscene on the real dental scene, preferably in transparent mode on thereal dental scene, thus allows the change between the updated instantand the simulation instant to be easily detected.

When an indicator represents a non-visible part of a physical element ofthe real dental scene, for example a root of a tooth, the informationrelating to this indicator is preferably included in the referencemodel. For example, the reference model can be a model of the dentalarch in which the crowns of the teeth, but also the roots of the teeth,are modeled, for example by means of a cone beam scanner. The methodaccording to the invention thus allows the operator to view parts of thedental arch of the patient which are not visible on the real dentalscene. Advantageously, these non-visible parts are represented in theirreal relative position with respect to the physical elements of the realdental scene. For example, the operator sees the roots and the nerves ofthe teeth that he or she observes in the mouth of the patient. He or shecan thus avoid an interaction with a tool that he or she is manipulatingor adapt an orthodontic appliance to limit the risk of a collisionbetween the roots of adjacent teeth, and therefore limit the risk ofroot resorption. For example, in an injection by means of a syringe, theoperator can accurately introduce the needle, to reach a dental root,without touching a dental nerve. The pains felt by the patient arethereby limited.

In the step e), the virtual dental scene is presented, as a function ofthe reference image, overlaid on the real dental scene or on therepresentation of the real dental scene in the updated image.

The virtual dental scene can be directly projected onto the real dentalscene. For example, red light spots can be projected onto the teeth toidentify bonding zones for orthodontic attachments.

The virtual dental scene can be displayed on a screen.

When the screen is transparent, in particular in the embodiment in whichit is incorporated in glasses, the operator can thus observe the virtualdental scene on the screen and the real dental scene through the screen,in transparent mode behind the virtual dental scene.

When the screen is opaque, particularly in the embodiment in which thescreen is the screen of a cellphone, of a laptop computer, of a virtualreality headset or of a tablet, the operator can thus simultaneouslyobserve the updated image and the virtual dental scene on the screen.

The virtual dental scene can be sufficiently transparent to reveal thereal dental scene or the updated image under it.

Alternatively, the virtual dental scene can be opaque, so as not toreveal the real dental scene or the updated image which extends behindor under it. The opacity of the virtual dental scene is particularlyadvantageous for simulating a past or future dental situation, forexample for viewing the whitening of the teeth under the effect of atreatment for that purpose, or the movement of a tooth, for exampleunder the effect of an orthodontic treatment or in the absence of anorthodontic treatment, for example to view periodontoclasia of a tooth.When the virtual dental scene is presented on the updated image, it canbe added on top of the updated image or, in an equivalent manner, theupdated image can be replaced by an image reprocessed by computer toreveal the virtual dental scene.

“Presentation of the virtual dental scene overlaid on the representationof the real dental scene in the updated image” should therefore beunderstood to include any presentation showing the virtual dental sceneon the representation of the real dental scene, including the display ofa reprocessed image.

When the screen is the glass of a mirror, the operator cansimultaneously observe, on the screen, his or her reflection and thevirtual dental scene, overlaid on his or her reflection. In particular,the patient can view the effect of a dental treatment, therapeutic ornot.

The virtual dental scene is presented as a function of the referenceimage and therefore, indirectly, as a function of the updated image. Inparticular, it is positioned, or “framed”, with respect to the realdental scene as a function of the reference image.

The virtual dental scene is presented overlaid, or “in register”, withthe real dental scene or with the representation thereof on the updatedimage, which facilitates the comparison. In other words, the elements ofthe virtual dental scene which correspond to elements of the real dentalscene are substantially exactly overlaid on the latter or on therepresentations of the latter. Notably when the virtual dental scene ispresented in transparent mode, the differences between the real dentalscene or the representation thereof on the one hand and the virtualdental scene on the other hand thus appear clearly to the operator. Theindicators also present to him or her information facilitating analysisof the situation.

Preferably, to present the virtual dental scene in register on the realdental scene or on the representation thereof on the updated image,characteristic marks are identified on the updated image whose positionwith respect to the virtual dental scene is known. For example, ends ofteeth or characteristic forms of teeth are identified that arerepresented both on the updated image and on the virtual dental scene.The reference image from which the virtual dental scene was determinedcan in particular be used to identify the position of the characteristicmarks in the virtual scene. In the step e) (or C)), the representationsof these characteristic marks are then overlaid on the updated image andin the virtual dental scene, which allows the virtual dental scene to beaccurately positioned with respect to the characteristic marksrepresented on the updated image.

Preferably, the method then returns to the step c) (or A)), preferablyless than 30 seconds, less than 10 seconds, less than 5 seconds,preferably less than 3 seconds, preferably less than 1 s, less than 0.5s, less than 0.2 s, preferably less than 0.1 s after the step e) (orC)). Preferably, the cycle of the steps c) to e) (or A) to C)) isperformed in real time, uninterrupted.

Alternatively, in one embodiment, the method is completed at the end ofthe step e) (or C)), without returning to the step c) (or A)). Themethod is thus performed “on demand”, and not in real time.

APPLICATION EXAMPLES

Real Time Assistance in an Intervention on the Teeth

Notably when the image acquisition appliance is in the form of glasses,the invention can be used in an intervention on the teeth, by the dentalcare professional wearing the glasses.

In one embodiment, the method is used in the context of an operation ofstripping of a tooth, or of milling. Preferably, the virtual dentalscene represents the tooth in its final form, after the stripping or themilling to be performed. Preferably, the dental care professional seesthe outline of the tooth in its final form accurately overlaid, that isto say in register, on the real tooth. This information allows him orher to machine the tooth with perfect accuracy.

In one embodiment, the method is used to fix a dental attachment, or“bracket”, to a tooth. Preferably, the virtual dental scene representsthe attachment in its final position, after it has been fixed onto thetooth. Preferably, the dental care professional sees the virtual outlineof the attachment in its final position with respect to the real tooth.This information allows him or her to place the real attachmentprecisely overlaid with the attachment of the virtual dental scene, andtherefore position it on the real tooth with perfect accuracy.

The method can also be used to fix a decorative item to the teeth.

In the intervention, the invention allows the operator, in particular adental care professional, to access relevant information. Suchinformation is presented to him or her, preferably in real time,overlaid with the real dental scene that he or she observes directly oron the updated image. The invention thus makes it possible toconsiderably increase the quality of the analysis of the situation, and,if necessary, adapt an intervention accordingly.

Improving Observance and Use for Teaching Purposes

In one embodiment, the method is used to obtain a better acceptance ofthe treatment by the patient. In particular, it can be used to simulate,realistically, a dental treatment. Preferably, the image acquisitionappliance is then a cellphone, a laptop computer, a tablet or a mirror.

With a cellphone, a laptop computer or a tablet, the patient films thedental arches, as if taking a selfie. With a mirror, the patient ispreferably filmed through the surface of the mirror, which allows theupdated image to faithfully represent the reflection R observed by thepatient.

Overlaid with the updated images which follow one another on the screenof the telephone, of the computer or of the tablet, or overlaid with hisor her reflection on the mirror, the patient sees corresponding virtualdental scenes, which represent a step of the dental treatment at asimulation instant. For example, the simulation instant can be theinstant marking the start of the treatment and the virtual dental scenecan represent an orthodontic appliance that the patient is consideringwearing. The patient can then view his or her face after the orthodonticappliance has been put in position in his or her mouth. By turning thehead or by moving the cellphone, the laptop computer or the tablet, orby moving in front of the mirror, he or she can easily modify thedirection of observation, the virtual dental scene being adapted in realtime.

Preferably, the patient can modify the simulation instant by interactionwith the screen, for example by moving a virtual cursor. The virtualdental scene is adapted accordingly, notably to take account of theeffect of the treatment. By acting on the cursor, the patient can thensimulate the progress of the treatment, that is to say view, forexample, how the teeth will be moved and/or change color, notably in thecase of a teeth whitening treatment or if the teeth are subject to acoloring agent, for example if the patient smokes or drinks largequantities of tea or of coffee. The movement of the cursor thus allowshim or her to simulate an acceleration of time.

This simulation facilitates the decision-making by the patient andadvantageously constitutes an incentive to follow the treatment.

In one embodiment, the patient can modify the value of other parametersof the simulation. For example, he or she can modify treatment parametervalues.

For example, he or she can simulate

-   -   the effect of one or more orthodontic appliances, notably in        order to choose the one that best suits him or her;    -   the effect of a temporary or permanent stop to a current        treatment;    -   the effect of more or less strict observance of the instructions        received, notably to view the effect of a modification of the        frequency and/or of the duration and/or of the technique for        brushing the teeth, or the effect of a delay in changing an        orthodontic splint and/or of a delay in making an appointment        with the dental care professional.

He or she can thus simulate the effect of poor observance of the medicalprescription, which is a factor in improving observance.

In one embodiment, the virtual dental scene shows warnings, preferablyin the form of a message or of a highlighting of an element of thevirtual dental scene, for example by showing in red a zone which shouldbe brushed more carefully.

Generally, the invention can be used to assess the dental situation ofthe patient, notably to check the progress of a dental treatment,and/or, outside of the context of a dental treatment, to check a changeof color and/or of form and/or of the arrangement of the teeth or of thegums.

Analysis of a Changing Dental Situation

In one embodiment, the method is used to view the stripping undergone bya tooth, for example through bruxism. Preferably, the virtual dentalscene represents the tooth in its prior form, before the stripping.Preferably, the operator, generally the patient or the dental careprofessional, sees the outline of the tooth in its prior form overlaidon the real tooth or on the representation thereof on the updated image.This information allows him or her to immediately and accurately viewthe scale of this wear, notably when the virtual dental scene ispresented in transparent mode.

In one embodiment, the method is used to view a distortion of the gum,and in particular a recession of the gum. Preferably, the virtual dentalscene represents the gum in its initial form, before the distortionthereof. Thus, the operator, generally the patient or the dental careprofessional, sees the outline of the gum in its initial form overlaidon the real gum or on the representation thereof. This informationallows him or her to immediately and accurately view this distortion,notably when the virtual dental scene is presented in transparent mode.

Of course, the invention is not limited to the embodiments describedabove and represented.

In particular, the patient is not limited to a human being. A methodaccording to the invention can be used for another animal.

The invention is not limited to a method comprising steps a) to e). Inparticular, the search for a reference image is not essential to theimplementation of the invention. If a reference image is not available,the elements which make up the virtual dental scene can be positioned onthe real dental scene or the representation thereof, as a function ofthe updated image.

A virtual dental scene can be determined as a function of severalreference images obtained from several respective updated imagesacquired simultaneously or at different, for example successive, updatedinstants.

1. A device for implementing a method comprising the followingsuccessive steps: A) at an updated instant, acquisition, by means of acellphone or a tablet, of an updated image representing a real dentalscene; B) determination of a virtual dental scene as a function of therepresentation of the real dental scene on the updated image andidentification of an element of the virtual dental scene which does notcomply with an assessment criterion, and highlighting of this element inthe virtual dental scene and/or adding a message relating to saidelement to the virtual dental scene; C) display of the updated image ona screen and presentation of the virtual dental scene overlaid with therepresentation of the real dental scene on the updated image displayedon the screen, in transparent mode or not on said representation;wherein the patient acquires said updated image in the step A), andobserves the screen in the step C), the device comprising: a cameraconfigured to implement the step A); a processing unit configured toimplement the step B); a screen configured to implement the step C); theprocessing unit, the camera and the screen being configured tocommunicate with one another to implement said steps.
 2. A device asclaimed in claim 1, wherein the nature and/or the location and/or theappearance of elements of the virtual dental scene are determined as afunction of the nature and/or of the location and/or of the appearanceof elements displayed in prior virtual dental scenes, and/or as afunction of the time interval with said prior virtual dental scenes,and/or as a function of differences between the updated images ofsuccessive cycles A)-C).
 3. A device as claimed in claim 1, wherein theassessment criterion relates to the state of health of the patientand/or to the positioning of an orthodontic appliance worn by thepatient and/or to the condition of an orthodontic appliance worn by thepatient and/or to a cost for a dental treatment.
 4. A device as claimedin claim 1, wherein the message is an instruction to be followed by thepatient and/or by a dental care professional responsible for thepatient.
 5. A device as claimed in claim 1, comprising a series ofcycles of steps A) to C).
 6. A device as claimed in claim 9, wherein astep A) is repeated less than 5 seconds after the step C).
 7. A deviceas claimed in claim 1, wherein, after the step C), an orthodonticappliance is modified and/or the arch is adjusted and/or an item ispositioned according to the presentation of the virtual dental scene onthe real dental scene.
 8. A device as claimed in claim 1, wherein, thepresentation means is a screen and the camera is incorporated into acellphone.
 9. A device as claimed in claim 1, wherein the screen and theprocessing unit are incorporated in the cellphone.
 10. The use of amethod as claimed in claim 1 to simulate: the effect of one or moreorthodontic appliances on the teeth of the patient, the effect of atemporary or permanent stop to a current treatment, the effect of amodification of the frequency and/or of the duration and/or of thetechnique for brushing of the teeth, or the effect of a delay inchanging an orthodontic splint and/or of a delay in making anappointment with the dental care professional, the effect of a treatmentfor whitening the teeth or the effect of cigarettes, the effect of anapplication of an instruction, or to guide the placement of anorthodontic appliance or of a part of an orthodontic appliance or of adental implant or of a decorative item, or to assess a differencerelating to the position and/or the form and/or a dimension of one ormore teeth and/or of an orthodontic appliance between the referenceinstant and the updated instant, or between the simulation instant andthe updated instant, notably in the context of an orthodontic treatment,and/or indicate a target location of the dental arch, in particular onone or more teeth.